Electrical musical instrument



Nov. 11, 1941.

L. HAMMOND ELECTR'ICAL MUSICAL INSTRUMENT Filed June 28, 1940 PatentedNov. 11, 1941 UNITED STATES PATENT OFFICE 2,262,494 ELECTRICAL MUSICAL.vINSTRUMENT Laurens Hammond, Chicago, Ill.

Application June 28, 1940, Serial No. 342,839

16 Claims.

/ musical instrument is due to the fact that the intensity of the tonesproduced may be controlled by the nger touch, i. e., the instrument istouch responsive. This touch responsive eiiect may be obtained inelectrical musical instruments in a manner such asl that disclosed in myprior Patent No. 2,126,464, but the means therein disclosed to obtainthis effect is relatively costly, as several parts which are subject towear can be made quiet in operation only by the exercise of suitableprecautions. In the modied form of the keyingcircuit shown in Fig. 28 ofthis patent, and likewise disclosed in my prior Patent No. 2,126,682,the mechanical structure of the keying means is greatly simpliiled, andan instrument ,incorporating this simplied key circuit has been marketedfor some time under the name Novachord While, strictly speaking, theinstrument employing the key circuit of saidl Patent No. 2,126,682 isnot touchresponsive, musicians have discovered in playing thisinstrument that the touch "responsive effect may be obtained in ameasure by setting the controls such that the attack `is comparativelyslow. When the controls are set in this manner, the musician may play aselection in a manner such that the melody portion is rendered insustained tones while the accompaniment portion of the selection isVrendered in percussive tones, with the intensity of the percussive tonescontrolled by the players touch. When played in this manner, thesustaining pedal is operated to obtain proper phrasing. l

When played in a staccato manner, the length l of time that the key isheld depressed will determine the maximuminnsity o! the tone produced,because the attack is so slow that the tone does not reach its maximumintensity unless the key is held depressed for an appreciable length oftime. Thus, the notes played in a legato manner attain maximumintensity, while the notes played in a staccato manner fail to reachmaximum intensity, but attain an intensity determined by the type ofstaccato touch einployed. That is, ifrtheplayer uses an e 65 Otherobjects will appear from fast and light staccato touch, the tonesproduced will be of very low intensity, while it he uses a heavier,slower staccato touch the tones produced will be of intermediateintensity. If a slow or legato touch is employed, the tones will beproduced at the maximum intensity for a given setting of other controlsof the instrument.

'I'he effect obtainable by playing the melody portion of the selectionin a legato` manner and playing the accompaniment in a detached 0rstaccato manner, using the sustaining pedal for phrasing, is startlinglyunique because the listener obtains the impression that he is listeningto two instruments, one a sustained tone instrumentv such as a violin,horn or organ, and the other a percussive instrument such as a. piano,xylophone or the like. This ability to play a sustained tone melody witha percussive accompa` niment greatly enhances the musical eilectivenessof the instrument by providing the musician with means for producingnovel and in-A teresting music. T'he fact that the musician is able,bythe character of the touch employed in playing the percussiveaccompaniment, to control the intensity of the percussive tones, furtherenlarges the variety of effects which may be obtained.

My present vinvention is a greatly simplified form of the keying circuitdisclosed in said PatentNo. 2,126,682, but is based upon the generalprincipleof operation above described, whereby the attack of the tone ismade so gradual that its maximum intensity may, in a practical manner,be determined by the touch employed by the musician.

It is therefore a primary obiec't of my invention to provide a verysimple and effective touch responsivel key circuit for electricalmusical instruments.

A further object is to provide an improved k circuit for electricalmusical instruments in which a sustaining pedal may be employed to varythe rate o! decay o! the tones.

A further objectf'is' to provide an improved touch responsive keyingcircuit for electrical musical instruments, in which there is but asingle contact switch employed tor each key.

A further object is to provide 'a keying system for electricalmusicalinstruments in which a sustaining pedal may be operated to cause sus- Atained tones in one register, and tones having i normal decaycharacteristics in another registerY of theinstrument.

the following e panying drawing in which:

l showninFigurehand. fr

description, reference being had Figure 1 is a diagrammatic view ofrepresentative'portlons of an electrical musical instrument showing oneimproved form of key circuit;

Figure 2 is an illustrative' diagram/being asimpuned modmcnuon oftne/keying circuit Figure 3 is a circuit diagram showing the furthermodication of the ykeying circuit.

Refen'ing toFlgure 1, the instrument comprises an electrostaticgenerator assembly enclosed in a metal casing' of sheet steelor thelike, compris- 4ing a boxlike bottom III, having a rigid cover I2secured thereto by screws I4. The generator Vassembly comprises aplurality of vertical frame plates I i, which are heldin properly spacedrelation by a plurality of longitudinally extendingv barsii and rods2li. The generator assembly may be of the general construction disclosedin my prior Letters Patent No. 1,956,350, granted April y24, 1934. s

The assembly of frame plates I6 is supported upon a plurality of blocks22 oi' insulating material, andvis held infspaced relation from theycover I2 by similar insulating blocks 24. A plurality of shafts 26 arerotatable in suitable bearings mounted in the vertical frame plates It,and 'are rotated by means of a driving pinion 2l, carried -upon adriving shaft 30. The shaft 28 is driven at a very accurately maintainedconstant speed,` preferably by a synchronous motor conto the accom- Yswitch 3C is connected through aresistance 3l with an electrode 4l inthe form of a narrow metal strip rigidly xed in a metal tube 42 by means4oi' insulating bushings 44. The inner-ends of the electrodes 40 lieclosely adjacent the peripheries of their respective phonic wheels 34,each with its associated phonic wheel constituting a continuouslychanging variable condenser.

The electrode tubesl 42 are mounted for sliding movement` in bushings 4Bwhich -may be peened or otherwise rigidly secured to the cover I2, eachbushing being providedwith a set screw y 44 so that the dimensions ofthe air gaps between the inner ends of the electrodes. 4I) andtheperipheries of the phonic wheels may be adjusted, and theele'ctrodesclamped in adjusted position. The phonic wheels, their shafts, thevertical frame plates I 6 and all the metallic parts of the generatorassembly associated therewith are electrically interconnected so as toconstitute, in eiect, a single plate common to a plurality ofvcondensers, of which the electrodes 40 form the A other plates.

nected to the shaft by a flexible elastic coupling 'Ihe driving pinion2Q meshes with driven gears Q2, which are preferably resiliently coupledto their respective shafts 26 in the manner disclosed in, my aforesaidpatent.

l Phonic wheels or rotors. 34 are preferably rigidly'securedto theirrespective shafts 28, are vmade of brass or other suitable metal, andhave their peripheries suitably formed, so as to generate a complex waveform which may be translated into sound having a pleasing tone quality..In the drawing the peripheries of the rotorsfare illustrated as havingspaced projections l5. It will in the manner described in myaforesaid'patent.

be understood that in the usual form of the ine Astrument the number of,the projections 35 upon the rotors willbe correlated with their speed ofyrotation so that electrical impulses of the fre-- quencies of theAnotes of' the tempered musical scale may be generated.

The frame plates I6 are electrically connected together and haveconnected thereto a conductor which passes through a suitable insulatinggrommet secured in the cover I2. The conductor -50 is connected to thegrid of a vacuum tube 52 flows through the resistance 38 to charge acon- By suitably selecting the values of denser V6|. the resistance 38and condenser 60, the rate at which the 'potential upon the electrode 4Iwill be built up,kmay be accurately predetermined.

It wm be noted that one termina Iof battery B i is grounded. `Each ofthe condensers'il likewise has one plate connected to a conductor 62,which is grounded. A resistor 64 has one end connected to the conductor64 which connects the resistance 38 with the electrode 40. The

It is preferable that the'shapes of the notches y or toothlikeprojections 25 on'the phonic wheels be'such as to produce a wave havinga long series of harmonic partials of gradually decreasing amotherI endof the resistance 64 is connected to a contact Il of a switch 1l. Theother terminalV of switch Il is connected to the grounded conductor l2.The resistance 64 is preferably of consider- A ably higher value thanthe `resistance I8. A re- \"sistor 'I2 of value several-times as greatas that of plitude; although as previously stated, their' shape.

may-be such as to produce any desired tone qual- 1 ity." Generallyspeaking, however, a tone quality 'fairly rich in fundamental tone andhaving a large series of upper partials of gradually decreasingintensity will be fo d most practical in an instrument of this charac r.

v tween a switch the resistance 64` is permanentlyL connected be- Aterminal I and the grounded conductor C2. 'l

The circuit for the key DI is similar to that Vdescribed with referencevto the key D4; and similar reference characters have therefore been api.plied to the corresponding elements except that It win be understoodthat* more 'wm be one phonic. wh'eel for each tone to be produced, vandthat in an instrument having a full board there will be 88 phonicwheels.

plano key- 'Ihe instrument is provided with 'a suitable key- I boardorvmanual includingua key designated D4. representative of the keys. ofthe treble. register, and key DI, representatiye'of the keys of the bassregister. Each key is adapted to close a.'

single contact switch I6, one terminal of which is connected to a directcurrent potential source .shown as a battery B. The other terminal ofthe the grounded resistancev has'been designated Il instead of `|2a.ndthe switch parts have been marked. and 1l. -The key D4 is representativeof any key in the treble register of the instrument, while the key DI isrepresentative of any note in the bass register.

The switches 1l, 'Ii areA adapted be operated by a sustaining pedal 02suitably mounted .on a

pivot 84 and-returned to' normal position by a spring I6. l Thesustaining pedal is illustrated diagrammatically as having an insulatingbar 88 pivotally connected thereto. so that the latter will be e mentplayed in raised when the sustaining pedal 82 is depressed. The bar 88is provided with an aperture 00 for the contact arms of switches 10, anda relativelyl larger aperture 92, for the contact arms of switches 10.In this way, upon depression of the sustaining pedal 82, the bar 06 willbe raised, and during the initial portion vof its upward stroke willopen the switches 18, and upon continued upward movement thereof, willopen switches 10.

In operation the phonic wheels will be rotated at constant-speedcontinuously, and the instruthe manner of a piano or organ. Upondepression of a key, D4, for example, closure of the associated switch36 will cause a gradual rise in the potential of the associatedelectrode 40. The rate at which the potential on this electrode is builtup is determined by the values of the resistance 30 and condenser 60.During this period the effect of the leak to ground furnished by theresistance 64 will be relatively small because this resistance isconsiderably higher than resistance 38. As the potential of theelectrode 40 is raised, a signal of gradually increasing amplitude willbe impressed upon the conductor 50. The character of this signal will bepredetermined by the shape of the periphery oi the phonic wheel 34 whichis rot/ating adjacent the energized electrode 40. The degree ofamplication of the signal impressed through the conn ductor 50 upon thegrid of the vacuum tube of theiirst stage of the amplifier may becontrolled by the volume and tone control device 56, which may beactuated by means of a manual control, or, in addition, by a swell pedalof thetype disclosed in my copending application Serial No. 91,284,filed July 18, 1936.

Upon release of vthe key D4, the potential upon` the associatedelectrode 40 will drop gradually, due to leakage of the charge of thecondenser 60 through the resistance 64 and switch 68, 10 to the groundedconductor 62. As a result, the strength oi.' the signal in the conductor50 will decay gradually at substantially a logarithmic rate. Whenever itis desired to sustain the signal for a period longer than its normaldecay` period, the sustaining pedal 82 is depressed, thus opening theswitch 60, 10. Under these circumstances, the leakage of the charge fromthe condenser 60 will be very slow, the rate being determined by thevalues of the resistance 64 and 12 which form a series path to groundwhenever the switch 68, 10 is open. Since the resistor 12y may be ofhigh value relative to the resistor 64, the signal 4will decay veryslowly.

Depression of a key such as DI in the bass regto its maximum value,since during such brief interval that the key switch 36 is closed, thecondenser 60 will not have become fully charged because of the limitedcurrent flow through the resistor 36. On the other hand, if the key isheld depressed for an appreciable time interval, the current iiowthrough the resistor 38 will fully charge the condenser 60, and thus thepolarizing potential upon the electrode l40 will be raised to themaximum value.

The musician may, therefore, render musical selections to' give theeffect of touch responsiveister of the instrument will result inoperation similar to that described with reference to key D4. However,it is preferable that the value of the resistor 00 be slightly greaterthan that of the resistor 12, so that the decay of the bass tones.

will be at a slower rate than the decay of the tones in the trebleregister. By operating the sustaining pedal a suiiicient distance toopen only the switch 16, 18, the bass tones may be rendered sustainingwhile the tones of the treble register decay at the usual rate, whereasif the sustaining pedal is fully depressed, both the bass and trebletones will be sustained.

When the sustaining pedal 32 is depressed to the full extent, so as toopen both switches 10 and 18, the intensity of the tones produced may becontrolled to a reasonable degree by thelength of time that the keys areheld depressed. If the key is struck a very light, fast blow, thepolarizing potential upon the electrode 40 will not increase ness. Hecan readily obtain this eiect by holding depressed such keys as hewishes to have produce high intensity tones, and touching lightly andrapidly those keys which he wishes to have produce tones of lowintensity. Of course when playing the instrument in this manner, thesustaining/pedal would be depressed, usually to its full extent, so asto produce the sustaining effect on all notes. Under some circumstancesthe sustaining pedal may be operated to cause sustaining of the basstones only, in'which event the touch responsive eiect would be lesspronounced in the treble register, and notes in the treble registerwould therefore be played in an vorganlike manner.

The circuit arrangement shown in Fig. 2 is generally similar to that ofFigure l, and is illustrated as comprising keys El and E2 which areadapted, upon depression, to close switches |00 and |02 respectively.These switches make contact with the common bus bar |04, and areconnected by resistors Ri to their respective electrodes 40, theelectrode 40 being connected to ground by resistor R2 and a condenserCI.

A resistor R3 is connected between the electrode 40 and ground through aswitch |06', which is adapted to be opened upon depression of a sus-.-taining pedal |08. It will thus be apparent that the resistors R2 and R3are in parallel when the sustaining pedal is not depressed, so as topermit the polarizing potential on the electrode 40 to drop rapidly whenthe sustaining pedal is not depressed, since under these circumstancesboth the resistors R2 and-R3 constitute leakage paths for the charge onthe condenser Cl. When, however, the sustaining pedal |08 is' depressedand the switch |06 thereby opened, the resistor R2 forms the onlyleakage path for the discharge of the condenser CI, and the potential onthe electrode 40 will thus drop very slowly, producing a correspondinglysustained tone.

It will be understood that the key circuits will preferably be identicaland individual, except that a common busbar |011 may be used -for allkey circuits, and the portion of the switches |06which is moved by thesustaining pedal may likewisebe common to the switches |06 for all v.mining the rate of decay when the sustaining pedal is operated. Ofcourse the value of the condenser C| is a factor in each of thesetransactions. As illustrative of suitable values which may be selectedfor these resistors and for the condenser C|, the following havebeen-found to be satisfactory, although it will be understood that thevalues selected may be varied tosuit RI, 500,000 ohms;

the preferences of the player:

Apedal would open only the switches R2,'5 megohms; R3, 750,000 ohms: CI,.1

Excepting for cost limitations, the resistances RI, R2 and R3 l might-be made adjustable.

For ordinary commercialv production, however,V

values may readily be selected which will result in the production oftones with generally acceptable attack and d'ecay characteristics.

In Figure 3, I have illustrated a slightly modi- 'lled key circuit inwhich the keys GI and G4 operate switches III! and II2 respectively, and

the attack resistors RII are connected between the switches and theadjustable potential sourcef have any common-parts, the cost of theswitches would 'be slightly more than the cost of the switch structureof Figure 2, because in the latter,

encased.

and the changes in potential are specified merely in a relative. ratherthan absolute, sense.

It will also .be apparent that the condensers 8l andCI may be connectedbetween their electrodes and any point of fixed or'undulating directcurrent potential, instead of being connected directly between theirelectrodes and ground. It is therefore essential merely that theseoondensers be "effectively" connected between their electrodes andground, that is, that they be connected between their electrodes andsome point the potential of which relative to ground is predetermined.For similar considerations, "in specifying the charging and dischargingof thesecondensers, -these terms are used in a relative rather than anabsolute sense. 'I'he term "ground is also used merely as a referencePotential, and is not intended to imply an actual round potential.

While I have shown and described particular forms of my invention, itwill be apparent to those skilled in the art, that numerous alterathebus bar IM may be common to all of the key operated switches. 'I'hethree-position sus- F taining -pedal of Figure l could, .of course, be

incorporated with th'e keying circuits of Figures 2 and 3. If desired,two sustaining pedals could be provided,4 one -being effective to openthe switches |06 (or switches II6) associated with al1 lof the keycircuits, while the other sustaining J associated with the key circuitsof the bass register.

From the foregoing description, it will be clear that I have provided avery simple form of key circuit for electrical musical instruments, in

which a certain degree of touchresponsiveness in substantially the sameway.

tions and modifications may be made without departing from the basicprinciples thereof. I

therefore desire in the following claims to in clude such variations andmodifications by which substantially the same results may be obtainedvI'claim:

l. In an electrical musical instrument, the

combination of an element having a terminal ,the potential of whichdetermines the intensity with which a particular tc'ne is sounded, asource of potential having one pole thereof connected to ground, a key,a switch operable by said key. a resistor, means connecting the otherpole of said source toA said terminal through said switch and isobtainable. It will be apparent that the key f circuit may be used inany type of electrical musical instrument in whichthe intensity at whicha note is sounded, is determined by a direct current polarizingpotential impressed upon a terminal of the generator, or uponanelectrode of la vacuum tube used to control the transmission of thesignal from the generator, as shown inmy aforesaid Patent No. 2,126,682.

If it is desired to have the instrument capable of producing differingtone qualities, suitable filter circuits may be included in theamplifier and provided with control switches so that selectedfrequencies will be attenuated. Because the phonic wheels generate tonesrich in harmonies, the tone quality may be greatly varied! Vbyattentuating ,certain frequencies, which will result in giving theinstrument individualistic tone quality characteristics. Sincethe keyswitches 36 are in thedirect current portion of the circuit, there islittle possibility of producing objectionable transient frequencies inthe output circuit when they are opened and closed.

In the foregoing description and in the following claims, it is assumedthat'the polarizing source (the battery B) has its negative terminalgrounded, and that apositive potential is thus impressedY upon theelectrode of the generator.

' ,It will be understood -that the connections of the source maybereversed so that a negative potential is impressed :upon'the generatorelectrode with equivalent effects. `In the following claims, therefore,the direction of current ilow resistor when said switch is closed, acondenser connected between said terminal and ground, a relatively lowresistance circuit for discharging said condenser, a relatively highresistance circuit for discharging said condenser, a switch in said lowresistance circuit, and' a sustaining control element forming the onlymeans for operating said last-named switch.

2. In an electrical musical instrument, the combination of an elementhaving a terminal the potential of which determines the intensity withwhich a particular tone is sounded, a source of potential having onepole thereof connected to a` pointv of fixed potential, a key, a switchoperable by said key, a resistor, means connecting the other pole ofsaid source to said terminal through said switch and resistor when saidkey is operated, a condenser connected between said terminal and saidlpoint of fixed potential and thus arranged to be charged through saidconnecting means, a relatively low resistance circuit for dischargingsaid condenser, a relatively high of said source, a switch operable bysaid key and contacting with said bus bar, a first resistor connectingsaid switch to said terminal, a condenser and a second resistor inparallel connected between said terminal and the other pole of saidsource, a third resistor and a second switch in series therewithconnected between saidv terminal and said other pole of said source, anda sustaining pedal for operating said second switch.

4. In an electrical musical instrument having for an individual note aterminal, the electrical potential of which controls the intensity withwhich that note will be sounded, a key, a source of direct currentpotential having one pole thereof connected to ground, a switch operatedby said key to impress a potential from said source upon said terminal,a resistance element forming a connection between said switch and saidterminal, a condenser connected between said terminal and ground,adjustable resistance elements connected between said terminal andground, a sustaining pedal, and means operated by depression or saidsustaining pedal m adjust said adjustable resistance elements toincrease the resistance thereof.

5. In an electrical musical instrument oi the class described, thecombination of a condenser continuously variable'at the frequency of amusical tone, said condenser having a stationary part and a moving part,an ampliiler connected to the moving part of said condenser to amplifythe electrical potential changes produced therein, a source of directcurrent potential having a grounded terminal, a manually operable switchfor connecting the other terminal of said source to the stationary partof said condenser, a resistance element connected between said switchand the stationary part of said condenser, a fixed condenser connectedbetween the stationary part of said variable condenser and ground, asecond resistance element permanently connected between 'the stationarypart of said variable condenser and ground, a third resistance element,and optionally operable means for connecting said third resistanceelement in series with said second resistance element.

6. In an electrical musical instrument, the combination of a condensercontinuously variable at the frequency of a musical tone, said condenserhaving a stationary part and a moving part, an ampliiier connected tothe moving part of said condenser to amplify the electrical impulsesproduced therein, a source of direct current potential, a manuallyoperable single pole switch for connecting said source to the stationarypart of said condenser, a resistance element connected between saidswitch and the stationary part of said condenser, a fixed condenserconnected between the stationary part of said variable condenser andground, a second resistance element in a circuit connecting thestationary part of said condenser to ground, said second resistanceelement having a value greater change the effective resistance of saidcircuits than that of said iirstv resistance element, and l combinationof a plurality of electrostatic generators, means for translating intofor shunting said secated means for impressing energizing potentialsupon selected ones of said generators, and sel lectively operable meansfor controlling the rate of decay of the potential impressed upon saidgenerators, said last named means being selectively operable upon apredetermined group of sound the impulses produced by said generators,key operfor said pre-determined group ofgenerators, and movable inanother manner to change the effective resistances of said circuits forall ofsaid generators.

8, In an electrical musical instrument, the combination of a pluralityof electrically interconnected constantly rotating tone wheel rotorshaving projections upon their peripheral'edges, an'electrode for each ofsaid generators having a portion thereof located in close proximity tothe path of rotation of the projections of said rotors, means common toall of said rotors for amplifying potential variations in any one or aplurality of said rotors, means for translating said amplified potentialvariations into sound, an electrical potential source having a groundedterminal, a plurality of key operated switches tor selectivelyconnecting said source of potential to said electrodes, circuits eachincluding a resistance element for connecting said switches with saidelectrodes respectively, a condenser connected between each of saidelectrodes and the grounded terminal of said potential source, a highresistance element normally connected in parallel with said condenser,and optionally operable switch means for connecting an additionalresistor in series with said resistance element. -9. In an electricalmusical instrument of the type which comprises a plurality of rotatabletone wheels, one for each of the notes of the musical scale within thegamut of the instrument, and each having a plurality of spacedprojections about its periphery, means for rotating said tone wheels,,and in which an amplifier is connected to all of the tone wheels foramplifying potential variations thereon and supplying the ampliiiedsignal to electroacoustic translating means; thecombination of anelectrode associated with each of said tone wheels, a source ofpotential having a grounded terminal, a plurality of key operated singlepole switches for connecting the other terminal of said source to saidelectrodes respectively, electrical networks between said switches, saidelectrodes and ground,

each of said networks including a resistor connected between the switchand its associated electrode, a condenser having one plate thereofconnected to said electrode and having its other plate connected toground, a leak resistance element permanently connected to each of saidcondensers for gradually discharging it; and optionally operable meansfor increasing the effective value of the leak resistances associatedwith a` group of said condensers, thereby to increase the length of timenecessary to discharge the condensers of said group.

l0. In an electrical `musical instrument having a plurality ofelectrostatic generators and means for amplifying and translating intosound elec- .trical impulses produced thereby; means for individuallycontrolling the delivery of impulses from said generators to saidtranslating means for pre-determining the rate of attack of the tonesproduced by said translating means comprising: resistance means for eachgenerator effective to determine the rate of decay of the tone, acircuit individual to each of said resistance means to change theeffective resistance of said resistance means, each of said circuitsincluding a switch, and actuating means for said switches selectivelycontrollable to operate a pre-determined group of said switches or tooperate all of said switches.

ill. an electrical musical instrument of the class described, thecombination of two groups of generators, one group for generatingelectrical impulses oi'frequencies of the treble register of the musicalscale, the other group for generating frequencies of the bass registerof the musical scale, means individual to each of said generators forchanging therate of decay of thev impulses produced thereby, asustaining pedal, means operated upon movement of said sustaining pedala pre-determined distance to operate said decay .changing meansassociated with `generators of one of said groups, and to loperate thedecay changing means associated with generators of the other of saidgroups upon movement of said sustaining pedalan additional distance.

12. In an electrical musical instrument, the combination of a pluralityof electrostatic gener' ators having phonic wheels rotating at constantspeeds, there being one of said -generators for each of the notes of themusical scale within the spear-e4 Iectively shunting said condenser, asecond switch, a second circuit eiIectively shunting'said condenser andincluding said second, switch and a \resistance of value lower than saidhigh resistance, and a sustaining Pedal for operating said switch, a lowVresistance circuit\ ompleted by said switch-and connecting said so etosaid ter'- minal, a circuit including a high resistance effectivelyshunting said condenser, a second switch,

conducting means veilfectively shunting ii portion yof said highresistance and including said second gamut ofthe instrument,electrodes'respectively cooperable with said wheels, an ampliiierconnected to all of said phonic wheels so as to be responsive topotential changes thereof, means for translating the outputof saidamplier into sound,` a source of directcurrent', selectively operablemeans individual to each of said-'generalminal andground, a source ofpolarizing potential iixed relative to ground, a key-operated switch,

tors to impress the potential of said source uponV said electrodes, saidmeans including a condenser and resistance network lto control the rateof decrease of the potential impressed upon 4said electrodes, thereby tocontrol the decay of the 'tones produced by said translating means, 'anda single optionally operablemeans for changing the eiiective value ofresistance in the network associated with one o t said generatorsf ortochange the eiiectiveA values oirthe resistances in switch, and asustaining pedal for operating said second switch. f

15. In an electrical musical instrument having a terminal thepotentialof which relative, to

ground determines the; intensity oi.' a tone producedv by theinstrument, the combination Iof a condenser eiectively connected betweensaid tera low resistance circuit completed by said switch and connectingsaid source to-said terminal, a

high resistance and a lower resistance connected in parallel with -eachother and with'said con.-

said networks associated with said last named generatorand at least oneadditional generator. A

13. In an electrical musical instrument having a terminal the potentialof which relative to ground determines the intensity of a tone producedlby thevinstrument, the combination of a condenser eiectively connectedbetween said terminal and ground. a source polarizing potential fixedrelative to ground, a key-operated switch, allow resistancecircuitcompleted by said switch and connecting said source to saidterminal, a circuit includinga highresistance ei.'-

denser, and sustaining pedal operated means for opening the circuitthrough said lower resistance. y16. In an electrical musical instrumenthaving 'a terminal the potential of which relative to ground determinesthe intensity 'of a tone produced by the instrument, the combination oi4a condenser eiectively connected between said ter' minal and ground, asource of polarizing potential vil'zfxed relative to ground, a playingkey, a switch operable by said key, a low resistance circuit completedby said switch and connecting said source to said terminal, adjustableresistance means shunting .said condenser, a sustaining pedal, and meanscontrolled solely by said sustaining pedal to change the eilective valueof said adjustable resistance means.

LAURENS HAMMOND.

